Thus, an actuator, commonly known as a pneumatic actuator, comprises an actuator piston disc that is displaceable in axial direction between a first position (inactive position) and a second position (active/extended position). The displacement is achieved by controlling a supply of pressure fluid, such as pressurized gas/air, that acts on and drives the actuator piston disc. The actuator piston disc acts in its turn directly or indirectly on the object that is to be displaced, for example an engine valve, for controlling its position.
In the application having an engine valve, when the actuator piston disc is in the inactive position the engine valve is in contact with its seat, and when the actuator piston disc is in the active position the engine valve is open, i.e. located at a distance from its seat.
It is a known demand that the actuators shall have as low operational noise as possible, especially in engine applications, but it is however also known that actuator makes noise during operation. The operational noise is above all generated due to the fact that actuators comprises metal members moving at high velocities and in their respective end positions contact other metal surfaces, whereupon knocking noise is generated. One of the moving metal members is for instance constituted by a slide valve body that in one and the same body comprises a first inlet valve as well as an outlet valve and a hydraulic valve, as is described and disclosed in U.S. Pat. No. 8,973,541. This design entails that the slide valve body, in this connection, has a very large mass entailing a high noise when the slide valve body hits a stop surface in connection with the slide valve body takes it inactive position.